This application is a continuation of international patent application No. PCT/EP01/03517, filed Mar. 28, 2001, the entire disclosure of which is hereby incorporated herein by reference. Priority is claimed based on Federal Republic of Germany patent application No. DE 100 18 515.0, filed Apr. 14, 2000
The present invention relates to a brake pressure regulating device for vehicles, especially commercial vehicles.
A brake pressure regulating device having an electronic brake circuit and a pneumatic emergency brake circuit is known from EP 0 110 119 B1. When the brake system is intact, braking control occurs purely electronically, wherein the driver issues a brake command through an operating brake valve and actuates an intake valve and a discharge valve to pressurize or ventilate a brake cylinder. When the brake electronics are intact, an electro-pneumatically controlled solenoid valve, which may be referred to as a xe2x80x9cbackup valvexe2x80x9d and is arranged between a pneumatic outlet of the operating brake valve and that of the brake cylinder, locks the operating brake valve against the brake cylinder. When the brake electronics fail, pressure is supplied to the brake cylinder.
For pilot control, supply pressure is removed and discharged back into the atmosphere. Due to the high pressures, the mechanical stress and the wear of the backup valve are extremely high, especially with a diaphragm valve. This is because the pressure triggered by the operating valve is applied to the inlet of the backup valve, and the brake cylinder pressure acts on the outlet of the backup valve. Only in few instances are the two pressures equal, so that unwanted, loud depressurizing noises may occur when the brake is released. In fact, in a vehicle that is equipped with a traction control system (TCS), the brake operating valve pressure may even be zero when the TCS is engaged. If the vehicle is equipped with an ABS system, the electrically regulated pressure, i.e., the brake cylinder pressure, may be zero when the ABS is engaged. Even at normal brake pressure regulation, the pressures generally differ due to load-dependent regulation. Nevertheless, the backup valve should not open.
A similar brake pressure regulating device is also known from EP 0 250 738 B1.
A mean pressure control device with four locking elements is known from DE 27 57 539 C2.
The purpose of the invention is to provide a brake pressure regulating device that is improved with respect to wear and noise development.
This goal is accomplished with a brake pressure regulating device for vehicles, especially commercial vehicles, with an operating brake valve for presetting a brake pressure, which features an electric outlet for triggering brake pressure valves and a pneumatic outlet. A ventilation and/or bleed valve is provided that may be electrically-triggered by the operating brake valve to pressurize or to bleed a brake cylinder. A control valve, which is connected between the pneumatic outlet of the operating brake valve and the brake cylinder, and which locks the pneumatic outlet against the brake cylinder during electronic brake pressure control, and triggers the electronics during a failure. The control valve features a switching piston, which is pressurized by brake cylinder pressure (BZ) and operating brake valve pressure (BBV). A pressure selection device is assigned to the control valve, which features a high-pressure outlet and a lower pressure outlet, to which the higher or lower of the two pressures (BZ, BBV) is applied. Wherein, a first switching piston side is pressurized precisely with one of the two pressures (BZ, BBV), and the second piston side is pressurized on a partial surface with brake operating valve pressure (BBV) and on another partial surface with brake cylinder pressure (BZ). Advantageous embodiments and further developments of the invention are described herein.
The underlying idea of the invention is to reduce the pressure force resulting from the inlet pressure and the outlet pressure of the backup valve and affecting the xe2x80x9cswitching element,xe2x80x9d or the valve body of the backup valve.
Reducing the resulting pressure also reduces mechanical stress, which increases the serviceable life. Furthermore, noise developing from the cylinder space or the so-called xe2x80x9cpilot chamberxe2x80x9d of the backup valve when the brake is released is reduced. This eliminates the need for an additional muffler. In addition, the invention allows for the use of a compact component for backup activation and deactivation.
According to the invention, the valve body of the backup valve is a switching piston with a first and second switching piston side. The first switching piston side is pressurized with either brake operating valve pressure or with brake cylinder pressure, and the second switching piston side is pressurized on a first partial surface with brake cylinder pressure and on a second partial surface with brake operating valve pressure. Thus, the pressures affecting both sides of the switching piston cancel each other out. As a result, a reduction in the effective pressure force on the switching piston is achieved in comparison to the state of the art.
When the brake system is intact, the backup valve locks, i.e., the switching piston locks the operating brake valve against the brake cylinder, with brake pressure regulation occurring purely electronically through a ventilation valve and a bleed valve. Thus, the brake operating valve pressure is applied to the inlet of the backup valve, and the currently predominating brake cylinder pressure is applied to the outlet. According to the invention, the backup valve ensures that, when the brake system is intact, the greater of the two pressures acts on the first side of the switching piston, and one of the two pressures is applied to partial surfaces of the other side of the switching piston. The resulting pressure force presses the backup valve""s switching piston against the valve seat, i.e., the switching piston locks the operating brake valve against the brake cylinder.
Conversely, pneumatic brake pressure must be possible when the electronic brake control system fails or is impaired, i.e., the brake operating valve pressure must be fed through the backup valve to the brake cylinder. In this case, according to the invention, the lower of the two pressures is applied to the first side of the switching piston, thereby ensuring that the switching piston xe2x80x9cfeeds throughxe2x80x9d and the pressure connection between the operating brake valve and the brake cylinder opens.
According to a further development of the invention, a pressure selection device is provided, which features a high-pressure outlet and a lower pressure outlet. Depending on which of the two pressures is higher, the brake operating valve pressure is applied to the high-pressure outlet and the brake cylinder pressure to the low-pressure outlet, or vice-versa.
According to a further development of the invention, a solenoid valve is provided that feeds the high-pressure outlet to the first side of the switching piston when electronically controlled operating braking takes place, i.e., when the brake electronics are intact, and that feeds the low-pressure outlet to the first side of the switching piston when there is a problem with the brake electronics. This solenoid valve features an idle open and an idle closed inlet, with the higher pressure being supplied to the idle closed inlet and the lower pressure being supplied to the idle open inlet through the pressure selection device.
The solenoid valve features, for example, a spring-loaded solenoid armature that locks the pressure selection device against the switching piston when the low-pressure outlet is activated and the high-pressure outlet is inactivated.
According to a further development of the invention, the pressure selection device features a high-pressure selection valve and low-pressure selection valve. The high-pressure selection valve may, for example, be a spherical valve with a single sphere, which, depending on the pressure level, feeds the brake operating valve pressure and/or the brake cylinder pressure to the high-pressure outlet. The low-pressure selection valve may, for example, be a spherical valve with connected spherical bodies, between which the low-pressure outlet is located. Depending on the pressure level, one of the two valve bodies blocks the higher of the two pressures, so that the lower of the two pressures is always applied to the low-pressure outlet. Of course, other valve bodies and/or control elements may be used instead of spherical valve bodies.
Alternatively, the pressure selection device may also be comprised of several individual valves. For example, a group of diaphragm valves may be provided, which select the higher or lower pressure of the two inlet pressures, i.e., the brake operating valve pressure and the brake cylinder pressure.
According to a further development of the invention, the pressure selection device may be integrated into the backup valve, especially into the switching piston of the backup valve. This allows for a highly compact construction. Alternatively, a separate arrangement is possible.
The invention will be described in greater detail below, on the basis of exemplary embodiments associated with the drawing.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.